WEST LAFAYETTE, Ind. — D.J. Knox's eyes fixed on the end zone 50 yards away as he raced up the Mollenkopf Athletic Center sideline.

Knox faced no defender on the play — a simple offensive rep in the middle of Purdue's first preseason practice. Yet the junior running back remembers life without football too vividly. After missing all of last season with injury, he vowed to take nothing easy.

Purdue fans are eager to see Knox return to his sophomore form. The starter showed ability both between the tackles and as a receiver out of the backfield en route to nearly 600 combined yards.

Knox, on the other hand, wants more.

"The coaches have pushed me to the limits," Knox said. "The medical staff has pushed me to my limits and pushed me places I didn't even know I could take my body.

"I'm 110 percent that I might even be better. That's my mindset coming into it — that I'm going to be 1,000 times better."

The 5-7, 210-pound Knox is one of several running backs expected to see reps for Purdue. Among the team's top five carriers, each one brings a specific look and skill set to an offense known for production and unpredictability when the Brohm brothers used it at Western Kentucky.

So what can Knox be for Purdue in 2017?

"Anything he wants to be," said fellow running back Markell Jones.

"If you had told me he didn't play all of last year and had an ACL (tear), I wouldn't believe you," Jones said. "He's come back with a fire in his eyes and he's ready to go. I'm excited about what he's going to be able to do this year."

Knox tore that ACL in the final moments of the 2016 spring game. The injury cost him all of last season, though he was able to retain a year of eligibility by using a redshirt.

Knox's infectious enthusiasm resonates through huddles, from the sideline and even in drills. Joy seems to be his default setting. That wasn't necessarily the case, however, in the first weeks after Knox's injury.

He said the turning point came last fall when then-interim head coach Gerad Parker added Knox to the travel roster for away games. Parker wanted Knox's presence to permeate through a team adjusting to a coaching change during another frustrating season.

"I can't say I didn't have hard times," Knox said. "I had a lot of hard days trying to come to the reality that I'm not playing football right now.

"Coach Parker gave me the chance to come out and support the team and give a little juice to the team, because I feel like that's something I bring. I like to bring energy, be a funny guy, trying to get everybody hyped and in the mood to perform. He gave me that opportunity and it put me in a good place mentally."

Knox said another boost came in the spring, when running backs coach Chris Barclay considered him a starter. Incoming head coach Jeff Brohm said at the time that Knox "stood out" due to his work ethic.

Only three practices into camp the roles in a deep running back group remain unsettled. Brohm, however, likes what Knox has shown since the spring.

Knox, Jones, Brian Lankford-Johnson, Richie Worship, Tario Fuller and perhaps others could work their way to carries for Purdue as early as Week 1. Knox is no longer battling his own body to get on the field. Now he's competing to return to the top of the depth chart and stay there.

"We have a lot of guys that could probably start at any school around the country, to be honest, and any one of us could be the starter," Knox said. "That's what most of my fuel comes from.

"The other guys in the room provide so much competition. It's crazy to sit here and say I'm not going to watch film — I'm not going to try and get better.